July-August 2012

Viewing Tornado Impact as More Than Physical Magnitude

by Mitch Stimers

Ten years ago this fall, an F3 tornado tore a path straight through the heart of Ladysmith, a small Northern Wisconsintown. I grew up a few cities over, and spent many weekends at the Army Reserve unit in Ladysmith, so to me, it sure seemed like the event would impact the community deeply. But just how to describe the level of impact?

Does an EF-2 tornado impart the same impact in Sioux City, Iowa, as it does in Dallas, Texas? If a high-end EF-4 skims the outer edge of Mobile, Alabama, does it impact that community in the same manner as a similarly-sized funnel traveling the length of downtown Lincoln, Nebraska, on a football Saturday? Scales used to measure extreme geophysical events in terms of strength have focused primarily on the physicality of the event.

When we try to understand the severity of a disaster, it seems useful to provide a measurement that expresses the movement away from everyday life, as recovery and adjustments to extreme events are not a part of the routine of a community. By creating an index that describes that impact, I aimed to fill a gap in how people understand and perceive a tornado's impact on a community.

The 2002 Ladysmith, Wisconsin, tornado provided the impetus for that idea, and as I worked out the details on how this index would be calculated, I knew it had to be something that looked at specific conditions other than damage to structures that are then used to estimate the speed of wind gusts. I wanted to use the proxies we typically look for in the newspapers in the days and weeks following the event to describe perceived impact—the amount of damage done and the number of fatalities. In addition tothose considerations, it seemed to me that the overall social health of the community should be a factor in determining the severity of impact; the dynamics of the community impacted should also be considered.

Hazard researchers frame those dynamics in the concept of social vulnerability, defined as “a measure of both the sensitivity of a population to natural hazards and its ability to respond to and recover from the impacts of disasters.” I created a vulnerability index for each community in the United States, and that, combined with damage and fatality index, normalized by population of the community affected, were aggregated to produce the Tornado Impact–Community Vulnerability Index (TICV)—a method to be used to assign an impact score to a community in the wake of a tornado. Raw scores were broken into six classes (which I called “tornado categories,” or TCs), ranging from zero to five, with zero indicating no impact and five indicating the most devastating impact (Table 1).

Table 1. TICV Score Range and Impact Descriptors.

In a dataset of 981 communities intersected by tornado tracks (2000–2009) that I assembled for the development of the index, I found, as expected, that in general, the higher the EF-scale (EFS) rating the more severe the impact—but not always. Table 2 shows a comparison between the TICV and the EFS, and as can be seen, EF-0 to EF-2 tornados have the ability to cause impact ranging from “none” to “severe.” While conversely, EF-4s (categorized as “violent”) resulted in impact scores ranging from “devastating” all the way down to “light.” The most destructive of all, EF-5s, produced scores described as either “severe” or “devastating.” What does this tell us? When we take other factors besides physicality into account, we will see that violent storms may not always cause the worst impact, and in even the weakest storms, impact can be heavy.

Table 2. TC and EFS comparison.

In order take a closer look at how the TICV could help put an event into perspective, I examined the tornados that struck the communities of Ladysmith, Wisconsin (2002), Manhattan, Kansas (2008), Enterprise, Alabama (2007), and Greensburg, Kansas (2007), with EFS values of three, four, four, and five, respectively.

Damage from the 2008 Manhattan, Kansas, event in this case was localized along a path that did not touch every business and home in the community. Friends and neighbors whose belongings, shelters, and mental states remained unscathed had the ability to come to the aid of others. Homes were opened to provide temporary shelter. As the immediate aftermath was tended to, the fact that the community possessed a lower degree of vulnerability, as I had calculated in the vulnerability index, than many others means rebuilding can commence, in most cases, almost immediately.

Manhattan is more than twice the size, in terms of population (44,831), when compared to the other three communities mentioned. Described as “light impact,” the TC1 rating for the Manhattan event makes the statement that given this community's size and its low-moderate vulnerability, the resources should be present to facilitate a recovery.

Damage to the Amherst neighborhood was especially heavy (see photo), but reflecting on a visit to the area in the spring of 2009, one year after the event, I noted that while some construction continued, the majority of homes had been repaired or rebuilt. Businesses damaged farther along the path were mostly repaired, and the Kansas State University campus showed practically no signs of the twister's fury, save a few trees with less-than-full crowns. The community is large, resilient, and can absorb and recover from the event quickly; therefore, the impact as a whole was light.

Consider the Manhattan, Kansas, event at TC1 in comparison to the Enterprise, Alabama, event at TC3. Although half the population at 21,178, Enterprise still possesses much in the way of resources in the case of a severe event. However, it scored in the moderate vulnerability category. The damage done to the community was widespread, and with nine lives lost, a community of this size is sure to feel the impact both physically and emotionally.

With a smaller population generally comes a smaller physical size (as was assumed, with population standing as a proxy for size in the damage index calculation), and with that comes a greater probability that key resources could be taken out of the recovery loop immediately. Fewer buildings in which to house the newly rendered homeless and the possibility of key elements of infrastructure such as fire and rescue units and hospitals being damaged heightens the level of impact (although those elements are not considered in the TICV). The EFS rated both the Manhattan and Enterprise tornadoes as EF-4s, but given the description of each, clearly they cannot be seen as similar in terms of the impact on the individual communities, as the TICV categories demonstrate.

Ladysmith, Wisconsin, with 3,932 residents, has less than one-fifth the population of Enterprise and less than one-10th the population of Manhattan. The tornado that ripped through the town toppled 40 buildings and caused minor to severe damage to scores more as it exited at the east end of the community. Emergency crews from surrounding and similar-sized towns, as well as larger surrounding metropolitan areas, converged on the community almost immediately. And, as is often seen in immediate post-disaster settings, altruism played a key role in first response, with many people in the community coming to help their neighbors. While, thankfully, no deaths occurred in Ladysmith, $25 million in damage virtually shut down the community for weeks.

I conducted research in the community regarding the state of recovery in both 2003 and 2004. By 2004, it was found that 26 percent of the damaged structures were still not repaired, with most of those located in the heavy-hit downtown area of central Lake Street and Miner Avenue. By 2007, nearly all buildings that were damaged has been repaired or replaced, and the town seemed to have made a near-full recovery. However, as of early 2012, some lots still remain empty in both the downtown area, as well as in the neighborhood on the west end of the city. The TC3 rating applied to this event, in comparison to the previous two, indicates a community that was initially hit hard by the storm, and recovery took some time, not unlike Enterprise, but in terms of size and resources available, it was worse off than Manhattan.

Greensburg, Kansas, has turned into something of a laboratory for what a town can potentially become in terms of its impact on the environment. But the impact on the town and its inhabitants is the focus here, and that impact was devastating. Buildings devoted to human service, such as the hospital and city hall, were among those plucked away by the tornado. Most of the vehicles in town were ruined, and with 95 percent of the buildings destroyed and city government facilities gone, people were literally left with nowhere to go and no one to whom they could turn.

Since the 2007 tornado, approximately one-third of the residents have moved permanently, further weakening the recovery effort. In revisiting Greensburg two years after the event, I noted that much of the town looked, and “felt,” the same as it did during a visit one month immediately following the tornado. Long stretches of road through residential neighborhoods were dotted with vacant houses, empty lots appeared where houses and businesses once stood, and eerie images of stripped and skewed trees were scattered throughout. The Greensburg tornado landed in the highest TICV category, TC5. The impact descriptor for that category is “devastating,” and given the near-total destruction of the community, the massive federally directed response to the scene, the out-migration of residents, and the ongoing recovery as of this writing, a TC5 rating should seem perfectly plausible to most of us.

When comparing this event to the Manhattan, Enterprise, and/or Ladysmith tornadoes, the difference in the category levels becomes clear. Manhattan, rated at TC1, certainly felt the impact of the June 2008 tornado, but dispersed the recovery effort among the large population, and one year later, the vast majority of damage had been repaired. Enterprise and Ladysmith, both TC3s, were heavily impacted, and recovery took several years but was nonetheless achieved (Ladysmith) or is well on the way to being achieved (Enterprise).

This is not to say that those communities are not forever changed, but they have returned to what one could consider a usual day-to-day routine. Greensburg, as well as Hallam, Nebraska, and Paisley, Florida (two of the three other tornadoes rated TC5s by this scale from 2000–2009), were, in large part, quite literally ripped from the face of the earth. Enough was left to build again, and with support from surrounding communities as well as the intangible internal support structure of friends and neighbors that appears in the wake of a disaster, these communities remain. However, the impact of the devastating tornadoes that struck their cities lingers. Depending on the situation, the level of impact from a disaster can have different meanings for different people. It is hoped that this rating scale can help put these events, and their different meanings, into better perspective.

As our understanding of phenomenal weather events continues to increase, the drive to understand the complex dynamics of societal-environmental relationships needs to continue as well. Should a tornado run through an abandoned town, one in which no one has property of value, or in which no human connections to that place exist, then the impact on that area will be zero. However, with population increasing every day, and more and more people moving into non-rural communities, we are furthering the potential for tornadoes to move through built areas where property does matter, people are at risk for harm, and intangibles such as our attachment to place and community can be blown away in seconds. An index value cannot stop phenomenal weather events from occurring, but I hope that this research can provide a measurement by which communities and the people within them can gain an understanding of the level of impact of a destructive tornado.

As science pushes ever-forward in seeking to understand our Earth's physical processes, it must consider who and what they affect: people and the communities in which they live.

MITCH STIMERS, Ph.D., is in the Division of Business, Science and Nursing at Cloud County Community College, Concordia, Kansas.